U.S. software firms are the most successful companies of the 21st century. From software-as-a-service pioneers like Salesforce and Zoom to ads-powered giants such as Google and Facebook, software firms represent close to 30 percent of the S&P-500 index. But despite their ascendancy, these companies have an Achilles’ heel: they make costly and avoidable mistakes when they venture overseas. I know first-hand because I was a Europe-based executive at Google and Twitter from 2005 to 2016, when those companies first expanded abroad. Today I invest in software-as-a-service (SaaS) companies on both sides of the Atlantic.